Generally, a conventional filter for an apparatus for collecting dust has a cylindrical shape having a bottom plate. Thus, to get the resistance to the ventilation of the filter to a low level and to enlarge the area of filtration, a long filter with a large diameter is required. Accordingly, a cabinet of an apparatus for collecting dust, which cabinet has many filters, becomes large. Therefore, there is a problem such that a large space is required to install the apparatus for collecting dust.
As an example of a conventional apparatus for collecting dust, there is the following apparatus. The apparatus for collecting dust is comprised of a housing, a set of hollow filters disposed in the housing, and a device for shaking off dust from filters by means of jets for reverse cleaning. This device is disposed in the housing, wherein the device comprises a plurality of blowing tubes, which are arranged so that they correspond to the rows of the filters, a source for providing compressed air to each blowing tube, and a plurality of passages of the jets disposed at the blowing tubes, which passages correspond to the openings of each hollow filter. At least one of the areas of the opening of the passage of the jet, the resistance to ventilation of the passage of the jet, and the effective area of the wall for receiving a flow of air, which wall is disposed at the entrance of the passage of the jet, is set as a variable parameter. The variable parameter is varied along the blowing tubes, from the proximal ends to the distal ends of the blowing tubes, so as to equalize the amounts of the air from the jets of each passage. (See Patent Document 1.)
For this pulse-jet-type apparatus for collecting dust, which has the technical features explained in the above paragraph, when the compressed air is blown into the hollow filter, generally 5˜10 times more secondary air than the compressed air that is blown into the hollow filter is sucked into the filter with the compressed air, based on the ejector effect. Accordingly, the secondary air helps to shake off the dust from the filters.
For this conventional and pulse-jet-type apparatus for collecting dust, to have the height of the apparatus be reduced as much as possible, the distance between the short pipes forming the passages of the jets and the hollow filters is shortened. This configuration allows the compressed air to be definitely blown into the hollow filters. However, since the amount of the secondary air is decreased, there is a problem such that the performance for shaking off the dust from the filters is reduced.
Recently, to solve the problem, a pleated-type filter that has a pleated cylindrical body and that is used for an apparatus for collecting dust has been developed. The pleated cylindrical body is made by folding a filtering cloth having a sheet-like shape. Its pleats are directed in the longitudinal direction of the cylindrical body. (See Patent Document 2.)                Patent Document 1: Japanese Patent Publication Laid-open No. H07-16413        Patent Document 2: Japanese Patent Publication Laid-open No. H08-309137        